液液同轴离心式喷嘴自激振荡机理研究

Originated from spray oscillation problem in a liquid rocket engine, the self-pulsation in liquid-liquid swirl coaxial injectors is planned to be experimentally, numerically and theoretically investigated in the present project. Firstly, the characteristics of the self-pulsation are studied. The frequency, amplitude and dominated spatial modes are obtained and the occurrence criterion of the self-pulsation is established as well. Then the effects of operating conditions and geometry on the self-pulsation are studied and critical non-dimensional parameters of the self-pulsation are obtained. Secondly, the unsteady motion of the air core inside the injector is analyzed and the correlation between the air core motion and the self-pulsation is clarified. The interaction among the inner and outer films and the intervenient air core is analyzed and the evolution of the self-pulsation is revealed. Finally, a dynamic model, which considers the inner and outer films and the intervenient air core, is built. Based on the model, the intrinsic dynamic characteristics and response to perturbation from the air core inside the injector are studied. The mechanism of the self-pulsation is revealed and the ways that geometry and operating conditions affect the self-pulsation are clarified.

本项目针对液体火箭发动机液液同轴离心式喷嘴出现的喷雾振荡问题，拟聚焦液液同轴离心式喷嘴的自激振荡现象开展实验、理论及数值模拟研究。首先针对自激振荡现象本身特征开展研究，获得自激振荡的频率和强度、主导的空间模态，建立自激振荡判别准则。研究工况结构参数对自激振荡的影响，确定产生自激振荡的临界无量纲参数。随后，分析喷嘴内部气核运动的动态特征，阐明气核运动与自激振荡的相关性。分析自激振荡条件下内外液膜以及膜间气核之间的相互作用关系，明晰自激振荡的流场演化过程。最后，基于对自激振荡的已有认识，建立内外液膜-膜间气核动力学模型，明晰内外液膜-膜间气核的固有动力学特性以及对喷嘴内部气核扰动的响应过程，阐明工况结构参数对自激振荡的影响机制，全面揭示自激振荡的产生机理。

本项目计划针对我国实际液体火箭发动机中液液同轴离心式喷嘴出现的自激振荡现象开展研究，旨在掌握工况结构参数对自激振荡的影响，明晰自激振荡的流场演化过程及机理，并建立自激振荡模型。.项目研究期间，开展了大量的实验、数值模拟以及理论分析工作。具体地，主要针对自激振荡现象及其影响因素开展研究，通过背景光成像方法获得喷雾的瞬态图像，识别出了自激振荡喷雾与稳态喷雾之间的差别，确定了自激振荡的判别准则为喷雾在喷嘴附近的喷雾宽度存在明显主频的周期性震荡。掌握了内外喷嘴入口参数、内喷嘴缩进长度、内喷嘴外壁形状、外喷嘴出口圆角大小、内喷嘴长径比以及切向孔大小的影响规律。结果表明内喷嘴We数对震荡频率影响很小，震荡频率随外喷嘴We增大而增大；喷嘴缩进长度、外喷嘴圆角喷嘴长径比对自激振荡频率有一定影响，而喷嘴外壁形状则几乎没有影响。针对自激振荡的演化过程，通过数值模拟和实验获得了喷嘴内部以及喷嘴近场附近的流动规律。阐明了内外喷嘴液膜的形成过程以及准稳态条件下的基本流场规律，明晰了喷嘴内外液膜之间的相互作用关系。内外液膜之间存在一定的吸引作用，最终会对喷嘴的流量系数、出口液膜厚度产生影响。清晰描述了自激振荡的演化过程，主要表现为喷嘴出口涡结构周期性脱落引发压力场波动最终导致液膜震荡。获得了气核三维重构结果，分析研究了喷嘴内部气核的动态特性，探究了喷嘴内部气核运动与液膜稳定性之间的关联关系，发现在部分工况喷嘴气核的动态运动频率与自激振荡一致。最后，分析定位了自激振荡的产生原因可能是喷嘴出口周期性脱落所致，而诱因可能与喷嘴内部流动的扰动相关。开展了自激振荡的理论分析，建立了内外液膜是否撞击的理论条件。.项目研究成果已经应用到我国某型号火箭发动机以及国防科技大学试验场燃烧设备的故障诊断和优化设计。